The paper features the threespine stickleback species pairs, which have become a famous evolutionary model system in the last several decades. In a few British Columbia lakes, you can find not one but two different kinds of stickleback – a small slim “limnetic” form that eats zooplankton in open areas of the lake, and a large deep-bodied “benthic” form that eats small invertebrates on the lake bottom.

A lot of work has already been done on the stickleback species pairs, but Harmon and the others took things in a new direction and examined whether these two specialized sticklebacks could affect the lake environment itself — in other words, are sticklebacks ecosystem engineers?

To answer the question, the researchers set up large outdoor tanks using sediment and small invertebrates from an actual stickleback lake. Then, they added fish: one set of tanks received only the limnetic, another received only the benthic, another received both limnetic and benthic, and the last set received generalist sticklebacks from a single-species lake.

The type of sticklebacks added to the tank had an effect on the invertebrate community – if the tank had limnetic sticklebacks(or limnetic+benthic), there were far fewer calanoidcopepods. There were also large differences between the generalist stickleback tanks and the species-pair tanks in primary production.

The most striking finding was that sticklebacks had an effect on the clarity of water; generalist sticklebacks had significant more transparent water than any of the other treatments, and species-pair treatments had the least clear water.

A lot more work will be required to uncover exactly how the sticklebacks are producing these effects, but it seems that the difference between one generalist stickleback and an adaptive radiation of two specialist sticklebacks can have important consequences for the habitats they live in.